3D datasets often convey significant information about the pore fluid fill of a prospect, through the presence of a seismic indicator, such as a bright spot, dim spot or AVO anomaly. This information can be used to significantly reduce the prospect risk, however, in many instances we find that the seismic indicator has a non hydrocarbon cause such as lithology. The challenge we therefore face as explorers, is the requirement to correctly risk these prospects taking into account all possible outcomes, avoiding any success case bias.

 

 

 


Relative amplitude stack

Data Courtesy of Gas della Concordia

 

 

 


AVO – intercept*gradient

Possible Outcomes?

• oil sand
• gas sand
• low saturation gas sand
• high porosity
• water sand
• volcanoclastics
• changes in encasing shales
• tuning

 

The Direct Fluid Indicator (DFI) Risk Modification methodology, provides a practical and straightforward approach to this problem that relies on a systematic Bayesian updating of risk estimates. The approach can be applied to ALL prospects and uses geological risk as its basis. A critical element of the method is generating a complete set of possible alternative non-success fluid and pore fluid fills that might produce the observed seismic indicator.

It encourages the consideration of prospect specific hydrocarbon visibility factors: What do I see? What might I expect to see? What alternative explanations are there for what I see?

Richard Houck published a paper in the Leading Edge (Houck, R. T., 1999, Estimating uncertainty in interpreting seismic indicators: The Leading Edge, 18, 320-325) which outlined how Bayesian Modification could be used to update geological risk to take into account the pore fluid information conveyed directly by seismic data. In 2000, Guy Smith and Simon Lunn of Enterprise Oil, devised a practical application of the methodology that could be applied to all prospects.

 In 2002 the DFI methodology developed by Guy Smith and Simon Lunn, was incorporated into GeoKnowledge’s GeoX risk and volumetrics software. Statoil and a number of other companies have adopted the methodology.

Download a free copy of the DFI Risk Modification Calculator